Mass transfer tool manipulator assembly

ABSTRACT

Systems and methods for transferring a micro device from a carrier substrate are disclosed. In an embodiment, a mass transfer tool manipulator assembly allows active alignment between an array of electrostatic transfer heads on a micro pick up array and an array of micro devices on a carrier substrate. Displacement of a compliant element of the mass transfer tool manipulator assembly may be sensed to control alignment between the array of electrostatic transfer heads and the array of micro devices.

BACKGROUND

1. Field

The present invention relates to micro devices. More particularly,embodiments of the present invention relate to systems and methods fortransferring a micro device from a carrier substrate.

2. Background Information

The feasibility of commercializing miniaturized devices such as radiofrequency (RF) microelectromechanical systems (MEMS) microswitches,light-emitting diode (LED) display systems, and MEMS or quartz-basedoscillators is largely constrained by the difficulties and costsassociated with manufacturing those devices. Manufacturing processestypically include wafer based processing and transferring techniques.

Device transferring processes include transfer from a transfer wafer toa receiving wafer. One such implementation is “direct printing”involving one bonding step of an array of devices from a transfer waferto a receiving wafer, followed by removal of the transfer wafer. Anothersuch implementation is “transfer printing” involving twobonding/de-bonding steps. In transfer printing a transfer wafer may pickup an array of devices from a donor wafer and bond the devices to areceiving wafer. Following transfer, the transfer wafer may be removedusing techniques that include laser lift-off (LLO), grinding orpolishing, and etching.

Gimbal mechanisms have been used in wafer polishing equipment tofacilitate evenly polishing a wafer. For example, passive gimbalmechanisms in polishing equipment facilitate alignment of wafers with apolishing pad.

SUMMARY OF THE DESCRIPTION

A mass transfer tool manipulator assembly and methods of using the masstransfer tool manipulator assembly to transfer an array of micro devicesfrom a carrier substrate are disclosed. In an embodiment, the masstransfer tool manipulator assembly includes a housing, a tip-tilt-zflexure, an actuator assembly, and a micro pick up array mount. A micropick up array may be provided separately from the mass transfer toolmanipulator assembly or integrally formed with the mass transfer toolmanipulator assembly. The tip-tilt-z flexure may include a top flexurecomponent joined with the housing and connected with a bottom flexurecomponent by a flexible coupling. For example, the top flexure componentand bottom flexure component may be flanges connected by the flexiblecoupling. The actuator assembly may be operably coupled with the bottomflexure component such that actuation of the actuator assembly moves thebottom flexure component relative to the top flexure component. Forexample, in an embodiment, the mass transfer tool manipulator assemblyincludes a distribution plate coupling the actuator assembly with thebottom flexure component. The micro pick up array mount may also becoupled with the bottom flexure component. Furthermore, the micro pickup array mount may include a pivot platform coupled with a compliantelement, such as a beam. A displacement sensor may be integrated withthe compliant element. In an embodiment, a micro pick up array having asubstrate supporting an electrostatic transfer head may be joinable withthe pivot platform.

In an embodiment, the micro pick up array mount may further include abase laterally around the pivot platform with the compliant elementbetween the pivot platform and the base and coupled with the pivotplatform and base at pivots. For example, the compliant element may becoupled with the base at an outer pivot on a base edge, and coupled withthe pivot platform at an inner pivot on a pivot platform edge that isorthogonal to the base edge. The compliant element may also be coupledwith the pivot platform at a second inner pivot across the pivotplatform from the inner pivot and coupled with the base at a secondouter pivot across the pivot platform from the outer pivot. In anembodiment, the micro pick up array mount may include a second compliantelement coupled with the base by the second outer pivot on a second baseedge and coupled with the pivot platform by the second inner pivot on asecond pivot platform edge. Furthermore, a second displacement sensormay be integrated with the second compliant element.

In an embodiment, the displacement sensor may be a strain gauge attachedto a high strain region of the compliant element near the inner pivot orthe outer pivot. For example, the strain gauge may be bonded to the highstrain region. Alternatively, the strain gauge may be deposited on thehigh strain region. Furthermore, the strain gauge may be formed bydoping the high strain region. In an embodiment, the micro pick up arraymount may include a reference strain gauge adjacent to the displacementsensor on the compliant element. The displacement sensor and thereference strain gauge may provide adjacent legs in a half Wheatstonebridge.

In an embodiment, the micro pick up array mount may include variouscontacts and electrical connections. For example, the micro pick uparray mount may include a displacement sensor contact on the base inelectrical connection with the displacement sensor. In an embodiment,the mass transfer tool manipulator assembly may include a positionsensing module in electrical connection with the displacement sensorthrough the displacement sensor contact. For example, the displacementsensor contact may be in electrical connection with the position sensingmodule through a flex circuit or a spring contact. In an embodiment, themicro pick up array mount may include a base operating voltage contacton the base in electrical connection with a pivot platform operatingvoltage contact on the pivot platform. Furthermore, the micro pick uparray mount may include a base clamp contact on the base in electricalconnection with a clamp electrode at a bonding site on the pivotplatform. In an embodiment, the micro pick up array mount may include abonding site on the pivot platform that includes a metal such as gold,copper, or aluminum.

In an embodiment, the micro pick up array mount may also include atemperature sensor and a heating element on the pivot platform. Theheating element may include a resistance alloy or a surface-mounttechnology resistor, for example. Furthermore, the mass transfer toolmanipulator assembly may include an insulation plate between the heatingelement and the position sensing module. The base of the micro pick uparray mount may be coupled with the insulation plate and the insulationplate may further be coupled with the distribution plate.

In an embodiment, a method includes moving a mass transfer toolmanipulator assembly toward a carrier substrate and contacting an arrayof micro devices on the carrier substrate with an array of electrostatictransfer heads coupled with a pivot platform of the mass transfer toolmanipulator assembly. The method may also include sensing deformation ofa compliant element coupled with the pivot platform. For example,sensing deformation may include sensing strain in a displacement sensorintegrated with the compliant element. In an embodiment, the methodfurther includes adjusting a position of a base coupled with thecompliant element after sensing deformation and before stopping relativemovement between the mass transfer tool manipulator assembly and thecarrier substrate. For example, adjusting the position may includeactuating an actuator assembly coupled to the base to further align thebase to a plane of the carrier substrate by tipping or tilting the base.The method may also include applying a voltage to the array ofelectrostatic transfer heads to create a grip pressure on the array ofmicro devices and picking up the array of micro devices from the carriersubstrate. In an embodiment, the method includes applying heat to thearray of electrostatic transfer heads while picking up the array ofmicro devices.

In an embodiment, a method includes moving a mass transfer toolmanipulator assembly toward a receiving substrate and contacting thereceiving substrate with an array of micro devices carried by an arrayof electrostatic transfer heads coupled with a pivot platform of themass transfer tool manipulator assembly. The method may also includesensing deformation of a compliant element coupled with the pivotplatform. For example, sensing deformation may include sensing strain ina displacement sensor integrated with the compliant element. In anembodiment, the method further includes adjusting a position of a basecoupled with the compliant element after sensing deformation and beforestopping relative movement between the mass transfer tool manipulatorassembly and the receiving substrate. For example, adjusting theposition may include actuating an actuator assembly coupled with thebase to further align the base to a plane of the receiving substrate bytipping or tilting the base. The method may also include removing avoltage from the array of electrostatic transfer heads and releasing thearray of micro devices onto the receiving substrate. In an embodiment,the method includes applying heat to the array of electrostatic transferheads before removing the voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustration of a mass transfer tool inaccordance with an embodiment of the invention.

FIG. 2 is a perspective view illustration of a mass transfer toolmanipulator assembly holding a micro pick up array in accordance with anembodiment of the invention.

FIG. 3 is a cross-sectional perspective view illustration of a masstransfer tool manipulator assembly, taken about section line A-A of FIG.2, in accordance with an embodiment of the invention.

FIG. 4A is a side view illustration of an actuator assembly having anactuator and a flexure attachment in accordance with an embodiment ofthe invention.

FIG. 4B is a perspective view of a tip-tilt-z flexure of a mass transfertool manipulator assembly in accordance with an embodiment of theinvention.

FIG. 5A is a perspective view of a micro pick up array mount having adisplacement sensor integrated with a compliant element in accordancewith an embodiment of the invention.

FIG. 5B is a plan view of a displacement sensor integrated with acompliant element of a micro pick up array mount, taken from detail X ofFIG. 5A, in accordance with an embodiment of the invention.

FIG. 6 is a perspective view of a micro pick up array mount having aheating element on a pivot platform in accordance with an embodiment ofthe invention.

FIG. 7 is a side view of a micro pick up array having a substratesupporting an array of electrostatic transfer heads in accordance withan embodiment of the invention.

FIG. 8 is a side view illustration of a micro pick up array mount joinedwith a micro pick up array in accordance with an embodiment of theinvention.

FIG. 9 is a perspective view of a micro pick up array mount having adisplacement sensor integrated with a compliant element and an array ofelectrostatic transfer heads on a pivot platform in accordance with anembodiment of the invention.

FIG. 10 is a perspective view of a micro pick up array mount having aheating element on a pivot platform in accordance with an embodiment ofthe invention.

FIG. 11 is a cross-sectional side view illustration of a micro pick uparray mount in electrical connection with a spring contact, taken aboutsection line B-B of FIG. 9, in accordance with an embodiment of theinvention.

FIG. 12 is a perspective view illustration of a micro pick up arraymount having a flexible region in accordance with an embodiment of theinvention.

FIG. 13 is a side view illustration of a mass transfer tool manipulatorassembly holding a micro pick up array and interconnected with a controlsystem in accordance with an embodiment of the invention.

FIG. 14 is a schematic illustration of a control loop to regulate a masstransfer tool manipulator assembly in accordance with an embodiment ofthe invention.

FIG. 15 is a flowchart illustrating a method of picking up an array ofmicro devices from a carrier substrate in accordance with an embodimentof the invention.

FIG. 16 is a schematic illustration of a mass transfer tool manipulatorassembly moving toward a carrier substrate in accordance with anembodiment of the invention.

FIG. 17 is a schematic illustration of an array of electrostatictransfer heads coupled with a mass transfer tool manipulator assemblycontacting an array of micro devices on a carrier substrate inaccordance with an embodiment of the invention.

FIG. 18 is a schematic illustration of a mass transfer tool manipulatorassembly adjusting a position of a micro pick up array mount inaccordance with an embodiment of the invention.

FIG. 19 is a schematic illustration of a mass transfer tool manipulatorassembly picking up an array of micro devices from a carrier substratein accordance with an embodiment of the invention.

FIG. 20 is a flowchart illustrating a method of placing an array ofmicro devices on a receiving substrate in accordance with an embodimentof the invention.

FIG. 21 is a schematic illustration of a mass transfer tool manipulatorassembly moving toward a receiving substrate in accordance with anembodiment of the invention.

FIG. 22 is a schematic illustration of an array of micro devices carriedby an array of electrostatic transfer heads coupled with a mass transfertool manipulator assembly contacting a receiving substrate in accordancewith an embodiment of the invention.

FIG. 23 is a schematic illustration of a mass transfer tool manipulatorassembly adjusting a position of a micro pick up array mount inaccordance with an embodiment of the invention.

FIG. 24 is a schematic illustration of a mass transfer tool manipulatorassembly releasing an array of micro devices onto a receiving substratein accordance with an embodiment of the invention.

FIG. 25 is a schematic illustration of computer system that may be usedin accordance with an embodiment of the invention.

DETAILED DESCRIPTION

Embodiments of the present invention describe systems and methods fortransferring a micro device or an array of micro devices from a carriersubstrate. For example, the micro devices or array of micro devices maybe any of the micro LED device structures illustrated and described inrelated U.S. patent application Ser. Nos. 13/372,222, 13/436,260,13/458,932, and 13/625,825. While some embodiments of the presentinvention are described with specific regard to micro LED devices, theembodiments of the invention are not so limited and certain embodimentsmay also be applicable to other micro LED devices and micro devices suchas diodes, transistors, integrated circuit (IC) chips, and MEMS.

In various embodiments, description is made with reference to thefigures. However, certain embodiments may be practiced without one ormore of these specific details, or in combination with other knownmethods and configurations. In the following description, numerousspecific details are set forth, such as specific configurations,dimensions, and processes, in order to provide a thorough understandingof the present invention. In other instances, well-known processes andmanufacturing techniques have not been described in particular detail inorder to not unnecessarily obscure the present invention. Referencethroughout this specification to “one embodiment,” “an embodiment”, orthe like, means that a particular feature, structure, configuration, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the invention. Thus, the appearances ofthe phrase “one embodiment,” “an embodiment”, or the like, in variousplaces throughout this specification are not necessarily referring tothe same embodiment of the invention. Furthermore, the particularfeatures, structures, configurations, or characteristics may be combinedin any suitable manner in one or more embodiments.

The terms “over”, “to”, “between”, and “on” as used herein may refer toa relative position of one layer or component with respect to otherlayers or components. One layer “over” or “on” another layer or bonded“to” another layer may be directly in contact with the other layer ormay have one or more intervening layers. One layer “between” layers maybe directly in contact with the layers or may have one or moreintervening layers.

The terms “micro” device or “micro” LED structure as used herein mayrefer to the descriptive size of certain devices or structures inaccordance with embodiments of the invention. As used herein, the terms“micro” devices or structures are meant to refer to the scale of 1 to100 μm. However, embodiments of the present invention are notnecessarily so limited, and certain aspects of the embodiments may beapplicable to larger and possibly smaller size scales. In an embodiment,a single micro device in an array of micro devices, and a singleelectrostatic transfer head in an array of electrostatic transfer headsboth have a maximum dimension, for example length or width, of 1 to 100μm. In an embodiment, the top contact surface of each micro device orelectrostatic transfer head has a maximum dimension of 1 to 100 μm. Inan embodiment, the top contact surface of each micro device orelectrostatic transfer head has a maximum dimension of 3 to 20 μm. In anembodiment, a pitch of an array of micro devices, and a pitch of acorresponding array of electrostatic transfer heads, may be (1 to 100μm) by (1 to 100 μm), for example, a 20 μm by 20 μm or a 5 μm by 5 μmpitch. In one aspect, without being limited to a particular theory,embodiments of the invention describe micro device transfer heads andhead arrays which operate in accordance with principles of electrostaticgrippers, using the attraction of opposite charges to pick up microdevices. In accordance with embodiments of the present invention, apull-in voltage may be applied to a micro device transfer head in orderto generate a grip pressure on a micro device and pick up the microdevice.

In an aspect, embodiments of the invention describe systems and methodsfor the mass transfer of micro devices using a mass transfer toolmanipulator assembly having a feedback mechanism for regulatingalignment of an array of electrostatic transfer heads with an array ofmicro devices on a carrier substrate. In an embodiment, a mass transfertool manipulator assembly includes a tip-tilt-z flexure, an actuatorassembly, and a micro pick up array mount having one or moredisplacement sensors integrated with one or more compliant elements. Forexample, the displacement sensors may be strain gauges attached to highstrain regions of the compliant elements. In this manner, thedisplacement sensors may be used to sense deformation of the compliantelements when an array of electrostatic transfer heads contact an arrayof micro devices. In an embodiment, based on feedback from thedisplacement sensor(s), the actuator assembly of the mass transfer toolmanipulator assembly may adjust a spatial orientation of the micro pickup array mount to change a center of pressure on the micro pick up arraymount. Thus, the mass transfer tool manipulator assembly may facilitateactive alignment of an array of electrostatic transfer heads mounted onthe micro pick up array mount with an array of micro devices based on aclosed feedback loop. Active alignment may increase the transfer rate ofmicro devices, since fine-alignment may be accomplished while pickingup, and similarly while releasing, the micro devices.

In another aspect, embodiments of the invention describe systems andmethods for the mass transfer of micro devices using a tip-tilt-zflexure coupled with an actuator assembly of a mass transfer toolmanipulator assembly. In an embodiment, the tip-tilt-z flexure imparts areactive load on the actuator assembly to smooth motion of a micro pickup array mount during adjustment by the actuator assembly. In anembodiment, the tip-tilt-z flexure imparts a restorative load on themicro pick up array mount to pick up an array of micro devices from acarrier substrate. Thus, the mass transfer tool manipulator assembly mayfacilitate contact with, and pick up, of an array of micro devices usingan array of electrostatic transfer heads without damaging the microdevices or the electrostatic transfer heads.

In another aspect, embodiments of the invention describe a manner forthe mass transfer of an array of pre-fabricated micro devices with anarray of electrostatic transfer heads. For example, the pre-fabricatedmicro devices may have a specific functionality such as, but not limitedto, a LED for light-emission, silicon IC for logic and memory, andgallium arsenide (GaAs) circuits for radio frequency (RF)communications. In some embodiments, arrays of micro LED devices whichare poised for pick up are described as having a 20 μm by 20 μm pitch,or 5 μm by 5 μm pitch. At these densities a 6 inch substrate, forexample, may accommodate approximately 165 million micro LED deviceswith a 10 μm by 10 μm pitch, or approximately 660 million micro LEDdevices with a 5 μm by 5 μm pitch. A mass transfer tool manipulatorassembly including an array of electrostatic transfer heads matching aninteger multiple of the pitch of the corresponding array of micro LEDdevices may be used to pick up and transfer the array of micro LEDdevices to a receiving substrate. In this manner, micro LED devices maybe integrated and assembled into heterogeneously integrated systems,including substrates of any size ranging from micro displays to largearea displays, and at high transfer rates. For example, a 1 cm by 1 cmarray of electrostatic transfer heads may pick up and transfer more than100,000 micro devices, with larger arrays of electrostatic transferheads being capable of transferring more micro devices.

Referring to FIG. 1, a perspective view illustration of a mass transfertool is shown in accordance with an embodiment of the invention. Asillustrated, mass transfer tool 100 may include a mass transfer toolmanipulator assembly 102 for picking up an array of micro devices from acarrier substrate held by a carrier substrate holder 104 and fortransferring and releasing the array of micro devices onto a receivingsubstrate held by a receiving substrate holder 106. Operation of masstransfer tool 100 and mass transfer tool manipulator assembly 102 may becontrolled at least in part by a computer system 108. In an embodiment,computer system 108 may control the operation of mass transfer toolmanipulator assembly 102 based on feedback signals received from varioussensors on a micro pick up array mount coupled with the mass transfertool manipulator assembly 102 as described in further detail below.

In an embodiment, components and subassemblies of mass transfer tool 100and mass transfer tool manipulator assembly 102 may be moved relative toeach other. For example, mass transfer tool 100 and mass transfer toolmanipulator assembly 102 may adjust spatial relationships betweencomponents in order to facilitate transferring an array of micro deviceswith an array of electrostatic transfer heads. Such adjustments mayrequire precise movements in multiple degrees of freedom. For example,mass transfer tool manipulator assembly 102 may include an actuatorassembly for adjusting a micro pick up array mount with at least threedegrees of freedom, e.g., tipping, tilting, and movement in a zdirection. Similarly, the carrier substrate holder 104 may be moved byan x-y stage 110 of mass transfer tool 100, having at least two degreesof freedom, e.g., along orthogonal axes within a horizontal plane. Thus,in an embodiment, an array of electrostatic transfer heads supported bymass transfer tool manipulator assembly 102 and an array of microdevices supported by a carrier substrate held by carrier substrateholder 104 may be precisely moved relative to each other with fivedegrees of freedom. However, mass transfer tool 100 and mass transfertool manipulator assembly 102 may include additional actuators thatprovide more degrees of freedom between the array of micro devices andthe array of electrostatic transfer heads, or between other componentsof the system. For example, mass transfer tool manipulator assembly 102may be mounted on an x-y stage that moves relative to x-y stage 110,establishing an additional two degrees of freedom between the array ofelectrostatic transfer heads supported by mass transfer tool manipulatorassembly 102 and the array of micro devices supported by the carriersubstrate held by carrier substrate holder 104.

Referring to FIG. 2, a perspective view illustration of a mass transfertool manipulator assembly holding a micro pick up array is shown inaccordance with an embodiment of the invention. FIG. 2 presents anoverview of the structural components of an embodiment of mass transfertool manipulator assembly 102. Mass transfer tool manipulator assembly102 may include a housing 210 coupled with a mass transfer tool mount200 of mass transfer tool 100. Housing 210 may have a columnarconstruction coupled with a tip-tilt-z flexure 230. An actuator assembly220 may be wholly or partially contained within housing 210, andfurthermore, actuator assembly 220 may be coupled with tip-tilt-zflexure 230 through a distribution plate 240. Distribution plate 240 mayalso be coupled with a micro pick up array mount 250. In an embodiment,micro pick up array mount 250 may be coupled with distribution plate 240through insulation plate 260, e.g., by retaining micro pick up arraymount 250 directly on insulation plate 260. In an embodiment, micro pickup array mount 250 may be joined with an intermediate component, e.g.,retainer plate 270, which is held against insulation plate 260 by aretaining ring 280. Furthermore, a micro pick up array 290 supporting anarray of electrostatic transfer heads may be integrated with micro pickup array mount 250.

Referring to FIG. 3, a cross-sectional perspective view illustration ofa mass transfer tool manipulator assembly, taken about section line A-Aof FIG. 2, is shown in accordance with an embodiment of the invention.FIG. 3 presents more detail of the mechanical interaction betweenstructural components of an embodiment of mass transfer tool manipulatorassembly 102. For example, actuator assembly 220 may include one or moreactuators 310 having a first actuator attachment 312 that may be fixedlycoupled with housing 210 and/or mass transfer tool mount 200. Actuator310 may further include second actuator attachment 314 moveable relativeto first actuator attachment 312. As described above, second actuatorattachment 314 may further be fastened with distribution plate 240.Thus, actuation of actuator 310 may cause relative movement betweendistribution plate 240 and housing 210.

Actuation of actuator 310 may therefore have at least two results.First, since micro pick up array mount 250 may be directly or indirectlycoupled with distribution plate 240, actuation of actuator 310 maychange a spatial relationship between micro pick up array mount 250, ormicro pick up array 290 joined with micro pick up array mount 250, andhousing 210. Second, since distribution plate 240 and housing 210 may becoupled with opposite ends of tip-tilt-z flexure 230, actuation ofactuator 310 may apply tensile, compressive, and/or torsional loads totip-tilt-z flexure 230 as distribution plate 240 moves relative tohousing 210.

In an embodiment, insulation plate 260 may be used to thermally isolatemicro pick up array mount 250 from other components of mass transfertool manipulator assembly 102. For example, insulation plate 260 may beplaced between micro pick up array mount 250 and actuator assembly 220,or other components of mass transfer tool manipulator assembly 102.Furthermore, contact between insulation plate 260 and micro pick uparray mount 250 or other components of mass transfer tool manipulatorassembly 102 may be minimized by limiting contact area between thecomponents. For example, insulation plate 260 may be coupled withdistribution plate 240 using insulating posts connected to thecomponents with fasteners, rather than coupling the components using aconductive coupling, such as a welded seam.

In an embodiment, insulation plate 260 may be formed from a materialexhibiting low thermal conductivity, e.g., thermal conductivity belowabout 1.5 W/m*° C. when heated to 200 degrees Celsius. For example,insulation plate 260 may be formed from an opaque fused quartz material,or another material having insulating properties. In an embodiment,insulation plate 260 is formed from a high purity opaque fused quartzmaterial containing uniformly distributed microscopic bubbles of lessthan about 20 micron, e.g., “Pyro-LD80” manufactured by Pyromatics Corp.headquartered in Mentor, Ohio. Thus, insulation plate 260 may functionas a thermal barrier to thermally isolate components of mass transfertool manipulator assembly 102 such as actuators 310 (e.g. piezoelectricactuators) and sensing module 316 from a heating element used to heatthe micro pick up array 290 supporting the array of electrostatictransfer heads as described in further detail below.

In an embodiment, retainer plate 270 and micro pick up array mount 250may be formed from materials have similar thermal expansioncoefficients. For example, micro pick up array mount 250 may be formedfrom silicon and retainer plate 270 may be formed from acontrolled-expansion nickel alloy, e.g., low expansion “Alloy 39”. Alloy39 is a controlled-expansion alloy that in an embodiment includes achemical composition of 0.05 C, 0.40 Mn, 0.25 Si, 39.00 Ni, Bal. Fe. Bycomparison, Alloy 39 exhibits a coefficient of thermal expansion ofabout 2 (×10-6/° C.) near 25° C., while silicon exhibits a linearcoefficient of thermal expansion of about 3 (×10-6/° C.) near the sametemperature. Thus, micro pick up array mount 250 and retainer plate 270need not have identical thermal expansion characteristics, but thosecomponents may expand and contract within the same order of magnitudewhen subjected to changing temperatures.

In an embodiment, retaining ring 280 may be fastened to insulation plate260, or directly to distribution plate 240, using clips, threadedfasteners, or other known fastening mechanisms. Furthermore, retainingring 280 may include one or more tabs or lips that press against micropick up array 290 or retainer plate 270 to clamp retainer plate 270against insulation plate 260 and couple micro pick up array mount 250with distribution plate 240. Other manners of retaining micro pick uparray mount 250 may be used. For example, retainer plate 270 may bebonded directly to insulation plate 260 using known adhesive or thermalbonding techniques, e.g., welding or soldering.

Referring to FIG. 4A, a side view illustration of an actuator assemblyhaving an actuator and a flexure attachment is shown in accordance withan embodiment of the invention. In an embodiment, actuator assembly 220includes at least one actuator 310 that creates motion between firstactuator attachment 312 and second actuator attachment 314. For example,actuator assembly 220 may include three linear actuators that each movefirst actuator attachment 312 relative to second actuator attachment 314in a single linear direction. Thus, actuator assembly 220 may create atotal of at least two degrees of freedom between mass transfer toolmount 200 coupled with first actuator attachment 312 and distributionplate 240 coupled with second actuator attachment 314. Moreparticularly, actuator assembly 220 may tip and tilt distribution plate240 relative to mass transfer tool mount 200. The quantity and type ofactuator 310, may be varied in actuator assembly 220 to change thedegrees of freedom and/or range of motion between mass transfer toolmount 200 and distribution plate 240, e.g., actuator 310 may be a rotaryactuator instead of a linear actuator. Accordingly, in an embodiment,actuator assembly 220 may provide a third degree of freedom in a zdirection by extending each of three linear actuators simultaneously.However, in another embodiment, additional degrees of freedom may beprovided by actuators external to mass transfer tool manipulatorassembly 102, such as by a single linear actuator of mass transfer tool100 that may move mass transfer tool mount 200 in a z direction.Similarly, as described above, x-y stage 110 may provide additionaldegrees of freedom between components of mass transfer tool 100 and masstransfer tool manipulator assembly 102. Thus, in an embodiment,actuation of distribution plate 240 may not depend solely on movement ofactuator assembly 220, but it may also depend on external actuators.

In an embodiment, actuator 310 may be a piezoelectric actuator. Althoughother linear actuators may be used, e.g., hydraulic, pneumatic, orelectromechanical actuators, a piezoelectric actuator may exhibit finepositioning resolution through relatively short movements whencontrolled by signals communicated through actuator lead 404. In anembodiment, actuator 310 may be a piezoelectric actuator with a range ofmotion of about 30 microns.

In an embodiment, first actuator attachment 312 may include firstflexure attachment 402. First flexure attachment 402 may include one ormore flexure relief 406. Flexure relief 406 may be configured to provideflexibility to first flexure attachment 402 in directions other than thedirection of motion of actuator 310. For example, flexure relief 406 mayinclude a channel machined in first flexure attachment 402 to provideflexibility in a direction orthogonal to the length of actuator 310.Furthermore, first flexure attachment 402 may provide movement withouthysteresis to counteract any backlash that may be present in actuator310. Actuator 310 and first flexure attachment 402 may be coupled with acoupling shaft 408 having ends that engage bores formed in actuator 310and first flexure attachment 402. Coupling shaft 408 may be allowed tofloat within the bores, or be rigidly fixed therein using known bondingand clamping methods.

Referring to FIG. 4B, a perspective view of a tip-tilt-z flexure of amass transfer tool manipulator assembly is shown in accordance with anembodiment of the invention. Tip-tilt-z flexure 230 may include a topflexure component 410 and a bottom flexure component 412. In anembodiment, top flexure component 410 and bottom flexure component 412are connected by a flexible coupling 414. Flexible coupling 414 may havenumerous configurations, for example, flexible coupling 414 may includea beam coupling or a helical coupling having one or more radial slot 416through a portion of a sidewall of tip-tilt-z flexure 230. In anembodiment, the radial slots 416 may be separated from each other by oneor more partition 418. Alternatively, radial slot 416 may be a singlehelically formed slot through tip-tilt-z flexure 230.

Flexible coupling 414 may be configured to allow top flexure component410 and bottom flexure component 412 to move relative to each otheralong a z axis 420 and about a tip axis 422 and a tilt axis 424.Resultantly, when top flexure component 410 couples with mass transfertool mount 200 through a rigid housing 210, and bottom flexure component412 couples with actuator assembly 220 through a rigid distributionplate 240, motion between top flexure component 410 and bottom flexurecomponent 412 minors the motion between mass transfer tool mount 200 anddistribution plate 240. Thus, tip-tilt-z flexure 230 allows actuatorassembly 220 to adjust distribution plate 240, as well as micro pick uparray mount 250 and/or micro pick up array 290 coupled with distributionplate 240, relative to mass transfer tool mount 200.

In addition to allowing the actuation of micro pick up array mount 250and/or micro pick up array 290 coupled with distribution plate 240,tip-tilt-z flexure 230 may facilitate such actuation in numerous ways.For example, a stiffness of flexible coupling 414 of tip-tilt-z flexure230 may be tuned to permit micro pick up array mount 250 to deform whencontacting a micro device on a carrier substrate. Also, the stiffness offlexible coupling 414 of tip-tilt-z flexure 230 may be tuned to smoothmovement of actuator assembly 220. Furthermore, the stiffness offlexible coupling 414 of tip-tilt-z flexure 230 may be tuned to providea pick up force that retracts a micro device gripped by an electrostatictransfer head 703 from a carrier substrate.

In an embodiment, flexible coupling 414 may be stiffer than thecompliant element of micro pick up array mount 250 described in furtherdetail below. Matching stiffness between flexible coupling 414 and thecompliant element in this way may permit the compliant element to deformas needed when an array of electrostatic transfer heads contacts anarray of micro devices. That is, rather than having the contact loadabsorbed by flexible coupling 414, the contact load may instead beabsorbed by a compliant element. Furthermore, the compliant element maydeform under such load and the deformation may be sensed by displacementsensor 518 integrated with the compliant element and used as feedback toadjust actuator assembly 220.

In an embodiment, flexible coupling 414 may provide a reactive load todistribution plate 240 as actuator assembly 220 moves distribution plate240. For example, in the case of tilting distribution plate 240 byactuator assembly 220 having three actuators, the kinematics of eachactuator may be slightly mismatched, resulting in unwanted jerkiness ortorsion, e.g., yawing, of distribution plate 240. The stiffness offlexible coupling 414 may be tuned to counteract this kinematic mismatchand resist unwanted movement. For example, in an embodiment, flexiblecoupling 414 having beam coupling as described above, i.e., havingpartitions 418 between radial slots 416, a torsional stiffness offlexible coupling 414 may be sufficiently high to prevent rotation aboutz axis 420 and thereby limit motion of distribution plate 240 entirelyto tipping and tilting about tip axis 422 and tilt axis 424.

In an embodiment, flexible coupling 414 may be expanded in length undera tensile load applied by actuator assembly 220, but the work exerted onflexible coupling 414 may result in potential energy being stored tocause a restorative load after deactivation of actuator assembly 220. Inother words, flexible coupling 414 may act as a tension spring to pullon distribution plate 240, and micro pick up array mount 250 coupledwith distribution plate 240, after removing the biasing load of actuatorassembly 220. In the case where the array of electrostatic transferheads 703 electrostatically grip an array of micro devices attached to acarrier substrate, the restorative load generated by flexible coupling414 may be greater than the load required to pick up the array of microdevices from the carrier substrate, i.e., the breaking pressure. Forexample, the breaking pressure may be expected to be about twoatmospheres in an embodiment, and thus, flexible coupling 414 may betuned to generate a restorative load equivalent to a pressure higherthan two atmospheres when extended. Thus, after the array ofelectrostatic transfer heads have been made to grip an array of microdevices, actuator assembly 220 may be deactivated and the pick uppressure may be provided by restorative loading from flexible coupling414.

In an embodiment, micro pick up array mount 250 includes sensors thatprovide feedback signals to a position sensing module 316 and/orcomputer system 108 through one or more electrical connections, such asflex circuit 318. As described below, feedback may include analogsignals from displacement sensors that are used in a control loop toregulate actuation of actuator 310, and therefore, spatial orientationof micro pick up array mount 250. Position sensing module 316 may belocated nearby micro pick up array mount 250 to reduce signaldegradation by limiting a distance that analog signals must travel froma displacement sensor to position sensing module 316. Position sensingmodule 316 may also be located on an opposite side of insulation plate260 to reduce heat transfer from micro pick up array mount 250 toposition sensing module 316 and actuators 310. Maintaining thermalisolation between position sensing module 316 and micro pick up arraymount 250 may reduce signal distortion caused by heat effects onposition sensing module 316. Maintaining thermal isolation betweenactuators 310, such as piezoelectric actuators, and micro pick up arraymount 250 may protect against thermal drift of the actuators 310 andconsequently the ability of the mass transfer tool manipulator assembly102 to accurately adjust the spatial orientation of the micro pick uparray mount 250 supporting the array of micro devices.

FIGS. 5A-6 and FIGS. 8-12 illustrate alternative embodiments of a micropick up array mount 250 that may be coupled with distribution plate 240to allow the spatial orientation of micro pick up array mount 250 to beadjusted when actuator assembly 220 adjusts distribution plate 240. Eachof the embodiments enable a spatial orientation of an electrostatictransfer head to be adjusted through articulation of micro pick up arraymount 250 or a micro pick up array 290. In an embodiment, micro pick uparray mount 250 may include any of the auto-aligning structuresillustrated and described in related U.S. application Ser. Nos.13/715,557 and 13/715,591, which are hereby incorporated by reference.

Referring to FIG. 5A, a perspective view of a micro pick up array mounthaving a displacement sensor integrated with a compliant element isshown in accordance with an embodiment of the invention. For the purposeof reference, the illustrated view may be referred to as a “front side”or “front face” of micro pick up array mount 250. In an embodiment,micro pick up array mount 250 includes base 502 and pivot platform 504.In an embodiment, base 502 surrounds all or a part of pivot platform504. For example, base 502 may extend laterally around pivot platform504. In an alternative embodiment, base 502 does not surround pivotplatform 504. Base 502 and pivot platform 504 may be interconnected byone or more compliant elements. For example, in the illustratedembodiment, a compliant element may be represented by beam 506. Beam 506may connect with base 502 and pivot platform 504 at one or more pivotlocations, such as inner pivot 508, 514 and outer pivot 510, 516. In anembodiment, inner pivots 508, 514 and outer pivots 510, 516 may belocated on edges of base 502 and pivot platform 504 that are orthogonalto each other.

In accordance with embodiments of the invention, micro pick up arraymount 250 may be formed from one or more portions or parts. For example,in an embodiment, base 502, pivot platform 504, and one or morecompliant elements (e.g. beam 506) may be formed from a silicon wafer toproduce distinct regions. More specifically, known processes, such asdeep etching, laser cutting, etc. may be used to form channels 522. Inat least one embodiment, channels 522 may therefore define the structureof micro pick up array mount 250 by providing separations between, e.g.,base 502, beam 506, and pivot platform 504 regions. For example,channels 522 may create a separation of about one hundred micronsbetween base 502 and beam 506, as well as between beam 506 and pivotplatform 504. Materials other than silicon may be utilized for the micropick up array mount 250, based on the ability of a material to deflectunder applied load, thermal stability, and minimal spring mass. Forexample, beside silicon, suitable material choices for forming a micropick up array mount 250 may include, but are not limited to, siliconcarbide, aluminum nitride, stainless steel, and aluminum.

Beam 506 may extend from inner pivot 508 to outer pivot 510 laterallyaround pivot platform 504. More particularly, beam 506 may conform tobase 502 and pivot platform 504 by fitting between those components andat least partially filling a void between those components. In anembodiment, the lateral extension of beam 506 provides a lever arm thatallows for bending and torsion in beam 506, inner pivots 508, 514, andouter pivots 510, 516, when forces are applied to pivot platform 504 orto a micro pick up array 290 mounted on pivot platform 504. Morespecifically, when a force is applied to pivot platform 504, such aswhen an electrostatic transfer head on a mounted micro pick up array 290contacts a micro device on a carrier substrate, pivot platform 504 maydeflect relative to base 502. This deflection may be accompanied by thedevelopment of one or more high strain areas, as represented by dottedline region Detail X, near outer pivot 510. Similar strain regions maydevelop near inner pivots 508, 514 and outer pivot 516 depending on thelocation that force is applied to pivot platform 504.

In an embodiment, beam 506 stiffness may be selected to facilitate bothpick up and placement of a micro device from a carrier substrate or areceiving substrate. For example, beam 506 stiffness may be tuned toensure that electrostatic transfer heads on pivot platform 504 are notdamaged after contacting micro devices on a carrier substrate, or aftermicro devices gripped by electrostatic transfer heads contact areceiving substrate. That is, beam 506 stiffness may permit beamdeformation sufficient to allow pivot platform 504 to deflect through acontact range. For example, in an embodiment, pivot platform 504 may beexpected to deflect upward at least thirty microns when electrostatictransfer heads contact an array of micro devices with a load less thanthe load required to damage electrostatic transfer heads.

In addition, beam 506 stiffness may be tuned to prevent plasticdeformation of beam 506 during pick up of a micro device from a carriersubstrate. For example, when an electrostatic transfer head grips amicro device on a carrier substrate, retraction of the mass transfertool manipulator assembly 102 may move base 502 upward relative to pivotplatform 504 associated with the electrostatic transfer head. Inessence, micro pick up array mount 250 acts like a tension springpulling the array of micro devices gripped by the array of electrostatictransfer heads. In an embodiment, beam 506 stiffness allows suchmovement without causing plastic deformation in beam 506. For example,in an embodiment in which an expected amount of about two atmospheres ofpressure is required to lift a micro device from a carrier substrate,beam 506 resists at least two atmosphere of pressure applied to pivotplatform 504 prior to being plastically deformed.

In an embodiment, one or more displacement sensors 418 may be integratedwith beam 506 at or near a high strain area. Displacement sensors 418may be capable of sensing beam 506 displacement resulting from loadsapplied to portions of micro pick up array mount 250, such as pivotplatform 504. For example, displacement sensors 418 may detect movementof beam 506 directly, or it may detect internal deformation to infermovement of beam 506.

Referring to FIG. 5B, a plan view of a displacement sensor integratedwith a compliant element of a micro pick up array mount, taken fromDetail X of FIG. 5A, is shown in accordance with an embodiment of theinvention. In an embodiment, displacement sensor 518 may be a straingauge that measures deformation of beam 506. The strain gauge mayexhibit an electrical resistance that varies with material deformation.More specifically, the strain gauge may be configured to deform whenbeam 506 deforms. That is, the strain gauge design may be selected basedon environmental and operating conditions associated with the transferof micro devices from a carrier substrate, to achieve the necessaryaccuracy, stability, cyclic endurance, etc. Accordingly, the straingauge may be formed from various materials and integrated with beam 506in numerous ways to achieve this goal. Several such embodiments aredescribed below.

A strain gauge may be separately formed from beam 506 and attachedthereto. In an embodiment, the strain gauge includes an insulativeflexible backing that supports a foil formed from polysilicon andelectrically insulates the foil from beam 506. The foil may be arrangedin a serpentine pattern, for example. An example of an attachable straingauge is a Series 015DJ general purpose strain gauge manufactured byVishay Precision Group headquartered in Malvern, Pa. A strain gauge thatis separately formed from beam 506 may be attached to beam 506 usingnumerous processes. For example, the strain gauge backing may bedirectly attached to beam 506 with an adhesive or other bondingoperation. More specifically, strain gauge backing may be fixed to asurface of beam 506 using solder, epoxy, or a combination of solder anda high-temperature epoxy.

In another embodiment, a strain gauge may be formed on beam 506 in adesired pattern, such as a serpentine pattern. In an embodiment, astrain gauge may be formed directly on beam 506 using a depositionprocess. For example, constantan copper-nickel traces may be sputtereddirectly on beam 506 in a serpentine pattern. The dimensions of a strandof a sputtered strain gauge having a serpentine pattern may be about 8micron width with about an 8 micron distance between strand lengths andmay be deposited to a thickness of about 105 nanometers.

In another embodiment, the material of beam 506 may be modified to forman integrated strain gauge. More specifically, beam 506 may be dopedwith a piezoresistive material to create a strain gauge within beam 506.As an example, the surface of beam 506 may be doped with silicon. Thedoped material may be in a serpentine pattern, having dimensions thatvary with an applied strain. Thus, the strain gauge may be fullyintegrated and physically indistinct from the remainder of beam 506.

In an embodiment, displacement sensor 518 may be a strain gauge on beam506 having a pattern (e.g. serpentine) of lengthwise strands that alignin a direction of anticipated strain. For example, beam 506 may beexpected to see compressive or tensile loads in a high strain area thataligns with channels 522 and thus the lengthwise strands of displacementsensor 518 may be parallel with channels 522. However, in an embodimentof micro pick up array mount 250 having compliant elements that seeprimary strain planes in other directions, displacement sensor 518 maybe oriented to detect such strains.

During the transfer of micro devices from a carrier substrate, beam 506and displacement sensor 518 may be subjected to elevated temperatures,and thus, temperature compensation may be necessary. In an embodiment,displacement sensor may be self-temperature compensated. Morespecifically, strain gauge material may be chosen to limittemperature-induced apparent strain over the operating conditions of thetransfer process. However, in an alternative embodiment, other mannersfor temperature compensation may be used. For example, temperaturecompensation may be achieved using a dummy gauge technique.

Still referring to FIG. 5B, in an embodiment, a dummy gauge techniqueutilizes a reference strain gauge 520 to compensate for displacementsensor 518. More particularly, reference strain gauge 520 may be locatednear displacement sensor 518 in the same area of strain. While strandsof displacement sensor 518 may align with the direction of appliedstrain, strands of reference strain gauge 520 may extend orthogonally tothe strands of displacement sensor 518 and to the direction of appliedstrain. Alternatively, reference strain gauge 520 may be located in anon-strain area of micro pick up array mount 250, apart fromdisplacement sensor 518, which is located in a high strain area of beam506. For example, reference strain gauge 520 may be located on base 502or pivot platform 504. Therefore, displacement sensor 518 may beconfigured to detect strain applied to beam 506 and reference straingauge may be configured to detect strain from thermal effects on micropick up array mount 250. Accordingly, a comparison of strain in bothstrain gauges may be used to determine, and compensate for, strainrelated to thermal expansion of beam 506.

Referring again to FIG. 5A, in an embodiment, reference strain gauge 520and displacement sensor 518 may be wired into adjacent legs of a halfWheatstone bridge to cancel out temperature effects between displacementsensor 518 and reference strain gauge 520. Each displacement sensor 518and reference strain gauge 520 may form a half Wheatstone bridge tosense strain in high strain areas near inner pivots 508, 514 or outerpivots 510, 516. However, each inner pivot 508, 514 and outer pivot 510,516 may include a second high strain area, opposite from the first highstrain area, and near a second lateral edge of the pivot defined bychannels 522. Another displacement sensor 518, or a pair of displacementsensor 518 and reference strain gauge 520, may be located in this secondhigh strain area to sense deformation. Furthermore, both pairs ofdisplacement sensor 518 and reference strain gauge 520 may be wiredtogether in a full Wheatstone bridge that may be monitored to determinethe material strain near the inner pivots 508, 514 and outer pivots 510,516. As described below, monitoring these strain signals may be used toinfer the pressure applied to pivot platform 504. Furthermore, strainsignals may be used by a control algorithm to determine the requiredtip, tilt, and z (orthogonal to pivot platform face) movement requiredto evenly distribute pressure across pivot platform 504.

Other types of sensors may be used to sense deformation or displacementin a compliant element of micro pick up array mount 250. For example,different strain gauge types, including capacitive strain gauges andstrain gauges that utilize fiber optic sensing may be used to sense beam506 deformation. Alternatively, displacement of either a compliantelement, or another component of micro pick up array mount 250, such aspivot platform 504, may be measured directly. In an embodiment, laserinterferometers may be used to sense displacement of a compliant elementor pivot platform 504. In another embodiment, capacitive displacementsensors may be used to sense displacement of a compliant element orpivot platform 504. Thus, numerous manners may be selected to measureand provide feedback related to displacement of a pivot platform 504 orcompliant element. In an embodiment, selection may be guided bytrade-offs such as cost, required accuracy, and environmentalconsiderations. For example, the ability to compensate for thermaleffects on a displacement sensor 518 may be one selection criteria.

In an embodiment, micro pick up array mount 250 includes one or morepivot platform operational voltage contacts 530 on pivot platform 504.Pivot platform operational voltage contacts 530 may function to transferan operating voltage to an array of electrostatic transfer heads onmicro pick up array 290 when operably connected with micro pick up arraymount 250. In an embodiment, pivot platform operational voltage contacts530 may be formed using a suitable technique such as, but not limitedto, sputtering or electron beam evaporation of a conductive material(e.g., metal) onto a surface of pivot platform 504.

In an embodiment, micro pick up array mount 250 may include one or morebonding sites for mounting micro pick up array 290. In an embodiment, abonding site includes one or more clamp electrodes 540 located on pivotplatform 504. More particularly, clamp electrodes 540 may be located onthe same surface of pivot platform 504 as pivot platform operatingvoltage contact 530. Clamp electrodes 540 may be constructed to secureor clamp micro pick up array 290 using electrostatic principles. Forexample, clamp electrodes 540 may include one or more conductive padscovered by a dielectric layer. In accordance with the principles ofelectrostatic grippers, when the conductive pads are maintained at avoltage and placed adjacent to metal or semiconductor film clamp areason micro pick up array 290, an electrostatic force clamps micro pick uparray 290 to micro pick up array mount 250. Here, the term adjacent mayrefer to the conductive pads being separated from the clamp areas onlyby a thin dielectric layer.

The components on the front face of micro pick up array mount 250 may beplaced in electrical connection with other components of mass transfertool 100 and mass transfer tool manipulator assembly 102 through variousleads. For example, front flex circuit 550 may extend from externalcomponents of mass transfer tool 100 and mass transfer tool manipulatorassembly 102 to electrically connect with front flex circuit connector552 on a face or edge of base 502. Front flex circuit 550 may be, forexample, a multi-conductor ribbon cable and front flex circuit connector552 may be a mating connector. Furthermore, front flex circuit connector552 may include terminal contacts from which various traces originateand extend to components on the front face of micro pick up array mount250.

As an example, displacement sensor 518 may be electrically connectedwith front flex circuit connector 552 through one or more displacementsensor trace 554. More particularly, displacement sensor 518 may beelectrically connected with two traces, an input and an output trace(FIG. 5B), that connect with separate terminal contacts of matingconnector. The one or more traces are graphically depicted as a singleline in FIG. 5A, and furthermore, traces are either omitted or shownwith broken lines to indicate that the number of actual leads has beenportrayed schematically for the sake of brevity in illustration.

Similarly, reference strain gauge 520 may be electrically connected withfront flex circuit connector 552 through one or more reference straingauge trace 556. Pivot platform operating voltage contact 530 may beelectrically connected with front flex circuit connector 552 through oneor more operating voltage trace 558. Clamp electrode 540 may beelectrically connected with front flex circuit connector 552 through oneor more clamp electrode trace 560. In an embodiment, traces may beformed directly on micro pick up array mount 250 using a suitabletechnique such as sputtering or e-beam evaporation. In an alternativeembodiment, traces may be a wire separate from, or bonded to a surfaceof, micro pick up array mount 250.

Referring to FIG. 6, a perspective view of a micro pick up array mounthaving a heating element on a pivot platform in accordance with anembodiment of the invention. For the purpose of reference, theillustrated view may be referred to as a “back side” or “back face” ofmicro pick up array mount 250. Micro pick up array mount 250 may includeone or more heating elements 602 over a back side of pivot platform 504of micro pick up array mount 250. In an embodiment, heating element 602may be formed from a resistance alloy, such as a nickel-chromium alloysputtered on micro pick up array mount 250. Thus, heating element 602may undergo Joule heating as electrical current passes through it.Therefore, heat may be transferred from heating element 602 to micropick up array mount 250 and/or micro pick up array 290 joined therewith.In an alternative embodiment, heating element 602 may be a surfacemounted resistor based on surface-mount technology that dissipates heatat a rate depending on a current applied to the resistor. In anembodiment, micro pick up array mount may be heated by an externalheating component, such as an infrared heating source directed towardpivot platform 504.

In an embodiment, micro pick up array mount 250 includes one or moretemperature sensors 610 to sense the temperature of micro pick up arraymount 250 or nearby structures, e.g., a micro pick up array 290. Forexample, temperature sensor 610 may be located on a back side of pivotplatform 504 to measure the temperature of the pivot platform 504. Forexample, temperature sensor 610 may be located in a center of pivotplatform 504, a corner of pivot platform 504, or on base 502 or beam506. Temperature sensor 610 may be a thermistor, thermocouple, or othertype of temperature sensor. Furthermore, temperature sensor 610 may bepotted or otherwise adhered or mechanically fixed to pivot platform 504.

In accordance with embodiments of the invention, heating element 602and/or temperature sensor 610 may be located on a front or back side ofmicro pick up array mount 250. The choice of location may be driven byconsiderations such as available space and whether the heating element602 and temperature sensor 610 will interfere with other functions. Forexample, the components may be placed to avoid disrupting electricalcharge in clamp electrode 540 of micro pick up array mount 250 orelectrostatic transfer heads of micro pick up array 290. Furthermore,the components may be placed to avoid interfering with bonding of micropick up array 290 to micro pick up array mount 250. Temperature sensor610 may be placed to closely approximate the peak temperature of micropickup array 290. Temperature offsets may be employed as necessary toachieve this approximation.

The components on the back face of micro pick up array mount 250 may beplaced in electrical connection with other components of mass transfertool 100 and mass transfer tool manipulator assembly 102 through variousleads. For example, back flex circuit 620 may extend from externalcomponents of mass transfer tool 100 and mass transfer tool manipulatorassembly 102 to electrically connect with back flex circuit connector630 mounted on a face or edge of base 502. Back flex circuit 620 may be,for example, a multi-conductor ribbon cable and back flex circuitconnector 630 may be a mating connector. Furthermore, back flex circuitconnector 630 may include terminal contacts from which various tracesoriginate and extend to components on the back face of micro pick uparray mount 250. As such, heating element 602 may be electricallyconnected with back flex circuit connector 630 through one or moreheating trace 640. Temperature sensor 610 may be electrically connectedwith back flex circuit connector 630 through one or more temperaturesensor trace 642. In an embodiment, traces may be formed directly onmicro pick up array mount 250 using a suitable technique such assputtering or e-beam evaporation. In an alternative embodiment, tracesmay be a wire separate from, or bonded to a surface of, micro pick uparray mount 250.

Referring to FIG. 7, a micro pick up array having a substrate supportingan array of electrostatic transfer heads is shown in accordance with anembodiment of the invention. Micro pick up array 290 may include a basesubstrate 702, formed from one or more of silicon, ceramics, andpolymers, supporting an array of electrostatic transfer heads 703. Eachelectrostatic transfer head 703 may include a mesa structure 704including a top surface 708, which may support an electrode 712.However, electrode 712 is illustrative, and in another embodiment, mesastructure 704 may be wholly or partially conductive, such that electrode712 may be unnecessary. A dielectric layer 716 covers top surface 708 ofeach mesa structure 704 and electrode 712, if present. A top contactsurface 718 of each electrostatic transfer head 703 has a maximumdimension, for example a length or width of 1 to 100 μm, which maycorrespond to the size of a micro device to be picked up.

Mesa structure 704 protrudes away from base substrate 702 so as toprovide a localized contact point of the top contact surface 718 to pickup a specific micro device during a pick up operation. In an embodiment,mesa structure 704 has a height of approximately 1 μm to 5 μm, or morespecifically approximately 2 μm. In an embodiment, mesa structure 704may have top surface 708 with surface area between 1 to 10,000 squaremicrometers. Mesa structure 704 may be formed in a variety ofgeometries, e.g., square, rectangular, circular, oval, etc., whilemaintaining this general surface area range. The height, width, andplanarity of the array of mesa structures on base substrate 702 arechosen so that each electrostatic transfer head 703 can make contactwith a corresponding micro device during a pick up operation, and sothat an electrostatic transfer head 703 does not inadvertently makecontact with a micro device adjacent to an intended corresponding microdevice during the pick up operation.

Still referring to FIG. 7, electrode lead 714 may place electrode 712 ormesa structure 704 in electrical connection with a terminal of operatingvoltage via 720 and with substrate operating voltage contact 722. Thus,an operating voltage may be transferred from substrate operating voltagecontact 722 of micro pick up array 290 to an array of electrostatictransfer heads 703 through operating voltage via 720. Operating voltagevia 720 may be formed in numerous manners. For example, operatingvoltage via 720 may be formed by drilling or etching a hole through basesubstrate 702, passivating the hole with an insulator, and forming aconductive material (e.g., metal) into the passivated hole to formoperating voltage via 720 using a suitable technique such as sputtering,e-beam evaporation, electroplating, or electroless deposition.

Micro pick up array 290 may include one or more substrate clamp contacts724 formed on a back side of micro pick up array 290. In one embodiment,substrate clamp contact 724 includes a conductive pad, such as a metalor semiconductor film. The conductive pad may be electrically isolatedfrom the other active regions of the micro pick up array 290. Forexample, insulating layers may be formed under, over, and around theconductive pads. In another embodiment, substrate clamp contact 724 maybe integrally formed with micro pick up array 290, for example byforming micro pick up array 290 and substrate clamp contact 724 frombulk silicon, and electrically isolating substrate clamp contact 724from the other active regions of micro pick up array 290.

Referring to FIG. 8, a cross-sectional side view illustration of a micropick up array mount joined with a micro pick up array is shown inaccordance with an embodiment of the invention. Micro pick up array 290and micro pick up array mount 250 may be physically and operably joined.As described above, in accordance with the principles of electrostaticgrippers and using the attraction of opposite charges, substrate clampcontact 724 of micro pick up array 290 may be aligned with, andelectrostatically retained by, clamp electrode 540 on micro pick uparray mount 250. More specifically, upon applying an electrostaticvoltage to clamp electrode 540 through clamp electrode trace 560, anelectrostatic gripping pressure will be applied to substrate clampelectrode 540, causing micro pick up array 290 to physically join withmicro pick up array mount 250. Furthermore, one or more substrateoperating voltage contacts 722 of micro pick up array 290 may be alignedwith, and placed adjacent to, pivot platform operating voltage contacts530. Thus, a voltage applied to pivot platform operating voltage contact530 through operating voltage trace 558 may be transferred throughsubstrate operating voltage contact 722 and operating voltage via 720 toone or more electrostatic transfer heads 703. Thus, micro pick up arraymount 250 and micro pick up array 290 may be electrically connected toenable micro pick up array 290 to generate an electrostatic grippingforce on an array of micro devices.

Heat may be delivered from micro pick up array mount 250 to micro pickup array 290 and/or to an array of micro devices gripped by micro pickup array 290 when those components are physically joined. Morespecifically, heating element 602 on micro pick up array mount 250 maybe resistively heated by delivering electrical current through heatingtrace 640. Thus, heat may be transferred from heating element 602through pivot platform 504 to micro pick up array 290. Furthermore, theheat delivered to micro pick up array 290 may dissipate through thearray of electrostatic transfer heads 703 into an array of micro devicesgripped by the array of electrostatic transfer heads 703.

The embodiments described above with regard to FIGS. 5A-8 thus far havecharacterized a configuration of micro pick up array mount 250 that maybe reversibly paired with micro pick up array 290. However, such aconfiguration is intended to be illustrative and not exhaustive. Forexample, an alternative embodiment of micro pick up array mount 250 mayinclude different modes of electrical connection with components of masstransfer tool 100 or mass transfer tool manipulator assembly 102.Furthermore, electrostatic transfer head 703 and/or micro pick up array290 may be alternatively joined with micro pick up array mount 250 indifferent manners. Additionally, the design of a compliant element inmicro pick up array mount 250 may be changed within the scope of theinvention. The following FIGS. 9-12 illustrate several alternativeembodiments in accordance with such variations.

Referring to FIG. 9, a perspective view of a micro pick up array mounthaving a displacement sensor integrated with a compliant element, and anarray of electrostatic transfer heads on a pivot platform is shown inaccordance with an embodiment of the invention. Most components of theembodiment of micro pick up array mount 250 shown in FIG. 9 are the sameor similar to those shown in FIG. 5A. However at least two substantialdifferences are described below. First, electrical connections betweenthe components on the front face of micro pick up array mount 250 areachieved differently. Second, rather than utilize a separate micro pickup array 290, the array of electrostatic transfer heads 703 are directlyintegrated with micro pick up array mount 250.

In an embodiment, component traces may terminate at voltage landing padson base 502 to make electrical connections. For example, displacementsensor trace 554 may interconnect displacement sensor 518 withdisplacement sensor landing pad 902. Similarly, reference strain gaugetrace 556 may interconnect reference strain gauge 520 with referencestrain gauge landing pad 904. Furthermore, operating voltage trace 558may interconnect electrostatic transfer head 703 formed on pivotplatform 504 with base operating voltage landing pad 906. The landingpads may be located on via structures that pass through base 502 from afront side to a back side of micro pick up array mount 250. Landing padsmay be formed using processes similar to those used to form traces,e.g., using sputtering processes.

In an embodiment, an array of electrostatic transfer heads are supporteddirectly by pivot platform 504. The structure and formation of the arrayof electrostatic transfer heads 703 may be the same or similar to thatdescribed above with respect to FIG. 7. For example, each electrostatictransfer head 703 may include mesa structure 704 with top surface 708covered by dielectric layer 716 and optionally supporting electrode 712.However, the array of electrostatic transfer heads are located on asurface of pivot platform 504 instead of micro pick up array 290surface. Furthermore, operating voltage traces 458 may replace electrodeleads 714.

Referring to FIG. 10, a perspective view of a micro pick up array mounthaving a heating element on a pivot platform is shown in accordance withan embodiment of the invention. In an embodiment, one or more contactsmay be located on base 502 and placed in electrical connection withcomponents of micro pick up array mount 250. Some of the base 502contacts may be placed in electrical connection with components on thefront side of micro pick up array mount 250. For example, displacementsensor contact 1002 may be located at a terminal of displacement sensorvia (FIG. 11) in electrical connection with displacement sensor landingpad 902. Similarly, reference strain gauge contact 1004 may be locatedat a terminal of a via (not shown) in electrical connection withreference strain gauge landing pad 904. Furthermore, base operatingvoltage contact 1006 may be located at a terminal of base operatingvoltage via (FIG. 11) in electrical connection with base operatingvoltage landing pad 906. Others of the base 502 contacts may be placedin electrical connection with components on the back side of micro pickup array mount 250. For example, heating contact 1008 may be placed inelectrical connection with heating element 602 through heating trace640. Similarly, temperatures sensor contact 1010 may be placed inelectrical connection with temperature sensor 610 through temperaturesensor trace 642.

Referring to FIG. 11, a cross-sectional side view illustration of amicro pick up array mount in electrical connection with a springcontact, taken about section line B-B of FIG. 9, is shown in accordancewith an embodiment of the invention. One or more of the contacts, e.g.,displacement sensor contact 1002 or base operating voltage contact 1006,may be pressed against spring contact 1106. Spring contact 1106 mayfurther be connected with components of mass transfer tool 100 or masstransfer tool manipulating assembly 102 through electrical connectionssuch as wiring leads and/or contact boards (not shown). Thus, numerousmanners are available to electrically connect components on micro pickup array mount 250 and components of mass transfer tool 100 or masstransfer tool manipulator assembly 102.

Referring to FIG. 12, a perspective view illustration of a micro pick uparray mount having a flexible region is shown in accordance with anembodiment of the invention. Most components of the embodiment of micropick up array mount 250 shown in FIG. 12 are the same or similar tothose shown in FIG. 5A. However at least two differences are describedbelow. First, in an embodiment, micro pick up array mount 250illustrated in FIG. 12 may be permanently joined with micro pick uparray 290. Second, in an embodiment, micro pick up array mount 250illustrated in FIG. 12 includes a compliant element without a beam 506.

In an embodiment, micro pick up array mount 250 and micro pick up array290 may be joined using one or more bonding pads 1202 to replace clampelectrode 540. Bonding pad 1202 may be formed of a variety of materialsincluding polymers, solders, metals, and other adhesives to facilitatethe formation of a permanent bond with another structure. In anembodiment, bonding pads 1202 may include gold, copper, or aluminum tofacilitate thermocompression bonding with an adjacent structure.However, thermocompression bonding represents only one manner of forminga permanent bond between structures, and bonding pad 1202 may includeother materials that facilitate the formation of a bond between themicro pick up array mount 250 and another part or structure with otherbonding mechanisms. For example, direct bonding, adhesive bonding,reactive bonding, soldering, etc., may be used at numerous bonding siteshaving various shapes and sizes.

To facilitate permanent bonding between micro pick up array 290 andmicro pick up array mount 250, substrate clamp contact 724 on micro pickup array 290 may be formed of a metallic material that facilitates athermocompression bond with bonding pad 1202, for example, both bondingpad 1202 and substrate clamp contact 724 may be formed from gold. Priorto permanently bonding micro pick up array mount 250 and micro pick uparray 290, pivot platform operating voltage contact 530 and substrateoperating voltage contact 722 may be aligned to allow the components tobe operably joined. After aligning the components, a permanentthermocompression bond may be formed to permanently join micro pick uparray mount 250 with micro pick up array 290.

In an embodiment, the compliant element of micro pick up array mount 250includes a singular surface not having beam 506. More specifically, acompliant element may be located between pivot platform 504 and base502, without being separated by channels 522. For example, a compliantelement may include flexible region 1204 delineated by a dotted line,which exists between pivot platform 504 and base 502. Flexible region1204 may be integrally formed with pivot platform 504 and base 502, butmay have different stiffness from those components. Alternatively, thedifference in stiffness may be due to varied structural characteristics,such as through forming flexible region 1204 with a thinnercross-section or a flexible form, e.g., as in the case of a bellows. Thereduced stiffness of flexible region 1204 may permit flexible region1204 to flex and allow relative movement between pivot platform 504 andbase 502. Thus, one or more displacement sensor 518 may be integratedwith flexible region 1204 to sense deformation of flexible region 1204.In an embodiment, electrical leads may be directly routed acrossflexible region 1204 of micro pick up array mount 250. For example,operating voltage trace 558 may cross directly through flexible region1204, as opposed to being routed around channels 522 as shown in theembodiment of FIG. 5A.

Having described several of the individual components of mass transfertool manipulator assembly 102, attention shall now be turned to theoverall function and control of the mass transfer tool manipulatorassembly 102. Referring to FIG. 13, a side view illustration of a masstransfer tool manipulator assembly holding a micro pick up array andinterconnected with a control system is shown in accordance with anembodiment of the invention. The illustrated system may be used toperform methods including the transfer of micro devices from carriersubstrate to receiving substrate. More specifically, the system may beused to actively control the spatial relationship between an array ofelectrostatic transfer heads 703 coupled with micro pick up array mount250 and an array of micro devices on a carrier substrate or a receivingsubstrate. Furthermore, the system may be used to control anelectrostatic gripping force between the array of electrostatic transferheads 703 and the array of micro devices. In addition, the system may beused to control heat delivered to the array of electrostatic transferheads 703, e.g., while the array of electrostatic transfer heads 703contacts the array of micro devices. Furthermore, the system may be usedto control retention of an array of electrostatic transfer heads 703against micro pick up array mount 250.

In an embodiment, actuation of actuator assembly 220, under the controlof computer system 108, affects motion of micro pick up array 290. Forexample, computer system 108 may be connected with an actuator powersupply 1302 directly or through intermediate controllers to providecontrol signals that cause actuator power supply 1302 to regulatemovement of one or more actuator 310, e.g., piezoelectric actuators, tomove distribution plate 240 coupled with micro pick up array mount 250.Micro pick up array mount 250 may retain micro pick up array 290. Suchregulation may be based on signals delivered from actuator power supply1302 to actuator assembly 220 through actuator lead 404.

In an embodiment, activating an array of electrostatic transfer headsprovides for electrostatic gripping of an array of micro devices. Forexample, computer system 108 may be connected with an operating voltagesupply 1304 directly or through intermediate controllers to providecontrol signals that cause operating voltage supply 1304 to deliver anelectrostatic voltage to electrostatic transfer heads through operatingvoltage lead 1306. Operating voltage lead 1306 may be integrated within,e.g., front flex circuit 550 or back flex circuit 620, to deliveroperating voltage as described above.

In an embodiment, heating of an array of electrostatic transfer headsmay be controlled by delivering power to heating element 602. Forexample, computer system 108 may be connected with heating voltagesupply 1308 directly or through intermediate controllers to providecontrol signals that cause heating voltage supply 1308 to deliver powerto heating element 602 through heating voltage lead 1310. Heatingvoltage lead 1310 may be integrated within, e.g., front flex circuit 550or back flex circuit 620, to deliver heating power as described above.

In an embodiment, micro pick up array 290 having an array ofelectrostatic transfer heads may be retained against micro pick up arraymount 250 by delivering an electrostatic voltage to clamp electrode 540.For example, computer system 108 may be connected with a clampingvoltage supply 1312 directly or through intermediate controllers toprovide control signals that cause clamping voltage supply 1312 todeliver an electrostatic voltage to clamp electrode 540 through clampingvoltage lead 1314. Clamping voltage lead 1314 may be integrated within,e.g., front flex circuit 550 or back flex circuit 620, to deliverclamping voltage as described above.

Control of the motion, electrostatic gripping, and heating functions ofmass transfer tool manipulator assembly 102 may be based on feedbackdelivered from sensors associated with micro pickup array mount. Forexample, temperature data may be provided from temperature sensor 610 tocomputer system 108 through, e.g., back flex circuit 620. Similarly,position-related data may be delivered from one or more displacementsensor 518 to computer system 108 through, e.g., front flex circuit 550.

In an embodiment, position-related data from displacement sensor 518 maybe input to, and transformed by, position sensing module 316 prior tobeing delivered to computer system 108. For example, position sensingmodule 316 or another component may apply an excitation voltage to oneor more displacement sensor 518, e.g., strain gauges, and an analogoutput voltage from displacement sensor 518 may be monitored by positionsensing module 316. The analog output voltages from the one or moredisplacement sensors may then undergo analog-to-digital processing byposition sensing module 316, and the resulting digital signals may beinput to computer system 108, or further processed through logicaloperations, to facilitate performance of a control algorithm forcontrolling motion of mass transfer tool manipulator assembly 102.

Referring to FIG. 14, a schematic illustration of a control loop toregulate a mass transfer tool manipulator assembly is shown inaccordance with an embodiment of the invention. In an embodiment, thecontrol loop may be closed to achieve the goal of evenly distributingpressure across micro pick up array mount 250. In other words, thecontrol loop may regulate mass transfer tool manipulator assembly 102 tochange the center of pressure on micro pick up array mount 250 to adesired location, e.g., to center pressure applied to pivot platform 504and evenly distribute pressure throughout the compliant element(s)surrounding pivot platform 504. Thus, setpoint 1402 may define a set ofreference signals that correspond to each displacement sensor 518sensing the same deformation in a respective beam 506. Displacementmeasurements from each displacement sensor 518 may be input to positionsensing module 316 as feedback related to a current state of pressuredistribution across micro pick up array mount 250. Position sensingmodule 316 may perform analog-to-digital signal processing andcalculate, or deliver processed signals to computer system 108 forcalculation of, e.g., an error signal. Based on the error signal,computer system 108 may use a control algorithm to determine appropriatecontrol signals to actuate actuator assembly 220 to achieve evendistribution of pressure across micro pick up array mount 250. Thesecontrol signals may be delivered directly to actuator assembly 220, orthey may be modified, e.g., by increasing control signal power, withamplifier 1404. Furthermore, the control signals may be fed directly toactuator assembly 220 or to actuator power supply 1302 for drivingactuator assembly 220. Displacement measurements from each displacementsensor 518 may continue to be monitored and fed into a control algorithmto continue to adjust actuator assembly 220 until output 1406 equalssetpoint 1402, i.e., until pressure evenly distributes across micro pickup array mount 250. This basic control loop model will be describedfurther below in relation to embodiments of methods for using masstransfer tool manipulator assembly 102 to pick up and place an array ofmicro devices.

In the following description, reference is made to FIGS. 15-24 whendescribing manners of operating a mass transfer tool manipulatorassembly to transfer an array of micro devices in accordance withembodiments of the invention. It is to be appreciated that the schematicillustrations provided in FIGS. 16-19 and FIGS. 21-24 are simplified twodimensional illustrations. For example, deflection of compliant elementssuch as schematic beams 1606, 1608 and actuation of the mass transfertool manipulator assembly 102 with a pair of schematic actuators 1602,1604 is illustrated and described in two dimensions. It is to beappreciated however, that deflection and actuation of the mass transfertool manipulator assembly 102 in accordance with embodiments of theinvention is not so limited. For example, as described above, variousactuators may be used to provide additional degrees of freedom, andthese degrees of freedom may not be fully represented by thetwo-dimensional depiction of FIGS. 16-19 and FIGS. 21-24. Moreparticularly, as shown in FIG. 4A, the actuator assembly 220 may includemore than two actuators, e.g., three actuators 310. In such a case,pivot platform 504 may be tilted or tipped in a third dimension about anaxis running across the page surface, which is not represented by FIGS.16-19 and FIGS. 21-24.

Referring to FIG. 15, a flowchart illustrating a method of picking up amicro device from a carrier substrate is shown in accordance with anembodiment of the invention. For illustrational purposes, the followingdescription of FIG. 15 makes reference to the embodiments illustrated inFIGS. 16-19. At operation 1501, mass transfer tool manipulator assembly102 moves toward carrier substrate. Referring to FIG. 16, a schematicillustration of a mass transfer tool manipulator assembly moving towarda carrier substrate 1601 is shown in accordance with an embodiment ofthe invention. Movement of manipulator assembly, and more specificallypivot platform 504, may be achieved by actuation of various actuators ofmass transfer tool 100 or by actuating both first schematic actuator1602 and second schematic actuator 1604 to extend in length.Electrostatic transfer heads 703 are schematically represented as beingmounted on pivot platform 504, although electrostatic transfer heads 703may instead be mounted on micro pick up array 290 retained against pivotplatform 504. As shown, pivot platform 504 may be undeflected relativeto base 502, and thus, both first schematic beam 1606 and secondschematic beam 1608 may be undisplaced or undeformed. In this initialstate, there may be a gap between array of electrostatic transfer heads703 and array of micro devices 1610 on carrier substrate 1601, e.g.,this snapshot may be prior to contacting array of micro devices 1610with array of electrostatic transfer heads 703. Here, the illustratedexaggeration of the gap indicates that pivot platform 504 and carriersubstrate 1601 may be misaligned with each other.

Referring again to FIG. 15, at operation 1505 array of micro devices1610 on carrier substrate 1601 may be contacted with array ofelectrostatic transfer heads 703 coupled with pivot platform 504 of masstransfer tool manipulator assembly 102. Referring to FIG. 17, aschematic illustration of an electrostatic transfer head coupled with amass transfer tool manipulator assembly contacting a micro device on acarrier substrate is shown in accordance with an embodiment of theinvention. In an embodiment, as pivot platform 504 approaches carriersubstrate 1601 out of alignment, an electrostatic transfer head 703nearest first schematic beam 1606 may contact a micro device 1610 beforecontacting a micro device 1610 with an electrostatic transfer head 703nearest second schematic beam 1608. Thus, first schematic beam 1606 maydeform, while second schematic beam 1608 may not.

Referring again to FIG. 15, at operation 1510 deformation of a compliantelement coupled with pivot platform 504 may be sensed. Referring againto FIG. 17, in an embodiment, as first schematic beam 1606 deforms,displacement sensor 518 (see FIG. 5A) generates a displacement signalassociated with first schematic beam 1606. The displacement signal maybe monitored and/or measured, e.g., by position sensing module 316. Forexample, the displacement signal may be fed back to position sensingmodule 316 to determine that deformation of first schematic beam 1606has occurred, and to calculate an error signal indicating the presenceof an uneven pressure distribution across pivot platform 504.

Referring to FIG. 18, a schematic illustration of a mass transfer toolmanipulator assembly adjusting a position of a micro pick up array mountis shown in accordance with an embodiment of the invention. Aftersensing deformation in first schematic beam 1606 and calculating anerror signal from the measured data, a control signal may be deliveredfrom computer system 108 to actuator assembly 220, causing secondschematic actuator 1604 to extend while maintaining first schematicactuator 1602 length. More specifically, second schematic actuator 1604may be extended to adjust the spatial orientation of pivot platform 504until the nearby electrostatic transfer head 703 contacts a micro device1610, e.g., once pivot platform 504 aligns with carrier substrate 1601.Furthermore, adjustment may be based on continued feedback signals fromdisplacement sensors associated with first schematic beam 1606 andsecond schematic beam 1608. That is, adjustment may continue until themeasured deformation in first schematic beam 1606 and second schematicbeam 1608 is approximately equal. At this point, the pressuredistribution across pivot platform 504 in the illustrated plane may beeven.

Referring again to FIG. 15, at operation 1515 relative movement betweenthe mass transfer tool manipulator assembly 102 and carrier substrate1601 stops. Referring again to FIG. 17, once pressure is evenlydistributed across pivot platform 504, actuation of actuator assembly220 according to control signals may be ceased. At this point, output1406 of the control loop may equal setpoint 1402. That is, the errorsignal may be zero or within a predefined range, indicating that thedeformation sensed by each displacement sensor 518 is approximatelyequal. This deformation value may be further defined through the controlloop to achieve a desired pressure between array of electrostatictransfer heads 703 and array of micro devices 1610. For example,sufficient pressure may be applied to ensure secure contact whileavoiding damage to electrostatic transfer heads 703 and micro devices1610 from excessive pressure application.

Referring again to FIG. 15, at operation 1520 a voltage may be appliedto array of electrostatic transfer heads to create a grip pressure onarray of micro devices. As shown in FIG. 18, with array of electrostatictransfer heads 703 placed in contact with array of micro devices 1610,an electrostatic voltage may be applied to electrostatic transfer heads703 through various contacts and connectors, e.g., operating voltagelead 1306, operating voltage trace 558, operating voltage via 720, etc.,of the mass transfer tool manipulator assembly 102, micro pick up arraymount 250, and micro pick up array 290. More specifically, voltage maybe transmitted from operating voltage supply 1304 to array ofelectrostatic transfer heads 703 based on control signals from computersystem 108. For example, the control signals may be based on a controlalgorithm instructing that electrostatic transfer heads be activated ifa predefined deformation is simultaneously sensed by each displacementsensor 518 during a pick up process. As a result, array of electrostatictransfer heads applies a gripping pressure to array of micro devices1610.

Referring again to FIG. 15, at operation 1525 array of micro device 1610may be picked up from carrier substrate 1601. Referring to FIG. 19, aschematic illustration of a mass transfer tool manipulator assemblypicking up a micro device from a carrier substrate is shown inaccordance with an embodiment of the invention. First schematic actuator1602 and second schematic actuator 1604 may be controlled by computersystem 108 to retract pivot platform 504 from carrier substrate 1601.During retraction, first schematic beam 1606 and second schematic beam1608 may return toward an undeformed state, as the beams release storedenergy and spring back to an initial configuration. Simultaneously,displacement sensors associated with the beams may transmit signals toposition sensing module 316 that indicate the beams are not deformed.However, at this stage a control algorithm may instruct that pivotplatform 504 be retracted further to clear the array of micro devices1610 for transfer to a receiving substrate. This retraction may beachieved through actuation of actuator assembly 220, or in anotherembodiment, through actuation of various actuators of mass transfer tool100. Furthermore, in an embodiment, retraction may be achieved bydeactivating actuator assembly 220 and allowing the inherent stiffnessof flexible coupling 414 of tip-tilt-z flexure 230 to restore tip-tilt-zflexure 230 to an initial state, which causes retraction of micro pickup array mount 250. During pick up, the electrostatic voltage suppliedto the array of electrostatic transfer heads may persist, and thus,array of micro devices 1610 may be retained on the electrostatictransfer heads 703 and removed from carrier substrate 1601.

During the pick up operation described with respect to FIG. 15, heatingelement 602 on micro pick up array mount 250 may be heated. For example,heating element 602 may be resistively heated to transfer heat to micropick up array 290 and to micro devices in contact with electrostatictransfer heads. Heat transfer may occur before, during, and afterpicking up the array of micro devices 1610 from carrier substrate 1601.

Referring to FIG. 20, a flowchart illustrating a method of placing amicro device on a receiving substrate is shown in accordance with anembodiment of the invention. For illustrational purposes, the followingdescription of FIG. 20 makes reference to the embodiments illustrated inFIGS. 21-24. At operation 2001, mass transfer tool manipulator assembly102 moves toward a receiving substrate. Referring to FIG. 21, aschematic illustration of a mass transfer tool manipulator assemblymoving toward a receiving substrate is shown in accordance with anembodiment of the invention. Movement of manipulator assembly, and morespecifically pivot platform 504, may be achieved by actuation of variousactuators of mass transfer tool 100 or by actuating both first schematicactuator 1602 and second schematic actuator 1604 to extend in length. Asshown, pivot platform 504 may be undeflected relative to base 502, andthus, both first schematic beam 1606 and second schematic beam 1608 maybe undisplaced or undeformed. In this initial state, there may be a gapbetween array of micro devices 1610 gripped by array of electrostatictransfer heads 703 and receiving substrate 2101, e.g., this snapshot maybe prior to contacting receiving substrate 2101 with array of microdevices 1610. Here, the illustrated exaggeration in the gap indicatesthat pivot platform 504 and receiving substrate 2101 may be misalignedwith each other.

Referring again to FIG. 20, at operation 2005 receiving substrate 2101is contacted with array of micro devices carried by array ofelectrostatic transfer heads coupled with pivot platform of masstransfer tool manipulator assembly. Referring to FIG. 22, a schematicillustration of a micro device carried by an electrostatic transfer headcoupled with a mass transfer tool manipulator assembly contacting areceiving substrate is shown in accordance with an embodiment of theinvention. In an embodiment, as pivot platform 504 approaches receivingsubstrate 2101 out of alignment, a micro device 1610 gripped by anelectrostatic transfer head 703 nearest first schematic beam 1606 maycontact receiving substrate 2101 before receiving substrate 2101contacts a micro device gripped by an electrostatic transfer headnearest second schematic beam 1608. Thus, first schematic beam 1606 maydeform, while second schematic beam 1608 may not.

Referring again to FIG. 20, at operation 2010 deformation of a compliantelement coupled with pivot platform 504 may be sensed. Referring againto FIG. 22, in an embodiment, as first schematic beam 1606 deforms,displacement sensor 518 associated with first schematic beam 1606generates a displacement signal. The displacement signal may bemonitored and/or measured, e.g., by position sensing module 316. Forexample, the displacement signal may be fed back to position sensingmodule 316 to determine that deformation of first schematic beam 1606has occurred, and to calculate an error signal indicating the presenceof an uneven pressure distribution across pivot platform 504.

Referring to FIG. 23, a schematic illustration of a mass transfer toolmanipulator assembly adjusting a position of a micro pick up array mountis shown in accordance with an embodiment of the invention. Aftersensing deformation in first schematic beam 1606 and calculating anerror signal from the measured data, a control signal may be deliveredfrom computer system 108 to actuator assembly 220, causing secondschematic actuator 1604 to extend while maintaining first schematicactuator 1602 length. More specifically, second schematic actuator 1604may be extended to adjust the spatial orientation of pivot platform 504until the nearby electrostatic transfer head 703 contacts a micro device1610, e.g., once pivot platform 504 aligns with receiving substrate2101. Furthermore, adjustment may be based on continued feedback signalsfrom displacement sensors associated with first schematic beam 1606 andsecond schematic beam 1608. That is, adjustment may continue until themeasured deformation in first schematic beam 1606 and second schematicbeam 1608 is approximately equal. At this point, the pressuredistribution across pivot platform 504 in the illustrated plane may beeven.

Referring again to FIG. 20, at operation 2015 relative movement betweenmass transfer tool manipulator assembly 102 and receiving substrate 2101may be stopped. Referring again to FIG. 23, once pressure is evenlydistributed across pivot platform 504, actuation of actuator assembly220 according to control signals may be ceased. At this point, output1406 of the control loop may equal setpoint 1402. That is, the errorsignal may be zero or within a predefined range, indicating that thedeformation sensed by each displacement sensor 518 is approximately thesame. This deformation value may be further defined through the controlloop to achieve a desired pressure between array of micro devices 1610and receiving substrate 2101. For example, sufficient pressure may beapplied to ensure secure contact while avoiding damage to micro devicesfrom excessive pressure application.

Referring again to FIG. 20, at operation 2020 a voltage is removed fromarray of electrostatic transfer heads. As shown in FIG. 23, with arrayof micro devices 1610 placed in contact with receiving substrate 2101,an electrostatic voltage may be removed from electrostatic transferheads 703. More specifically, operating voltage transmitted fromoperating voltage supply 1304 to array of electrostatic transfer heads703 may be discontinued based on control signals from computer system108. For example, the control signals may be based on a controlalgorithm instructing that electrostatic transfer heads 703 bedeactivated if a predefined deformation is sensed in each displacementsensor 518 simultaneously during a placement operation. As a result,array of micro devices 1610 are released from array of electrostatictransfer heads 703.

Referring again to FIG. 20, at operation 2025 array of micro devices1610 may be released onto receiving substrate 2101. Referring to FIG.24, a schematic illustration of a mass transfer tool manipulatorassembly releasing a micro device onto a receiving substrate is shown inaccordance with an embodiment of the invention. First schematic actuator1602 and second schematic actuator 1604 may be controlled by computersystem 108 to retract pivot platform 504 from receiving substrate 2101.During retraction, first schematic beam 1606 and second schematic beam1608 may return toward an undeformed state, as the beams release storedenergy and spring back to an initial configuration. Simultaneously,displacement sensors associated with the beams may transmit signals toposition sensing module 316 that indicate no deformation of the beams.However, at this stage a control algorithm may instruct that pivotplatform 504 be retracted further to clear the pivot platform 504 and tobegin another pick up operation. This retraction may be achieved throughactuation of actuator assembly 220, or in another embodiment, throughactuation of various actuators of mass transfer tool 100. Furthermore,in an embodiment, retraction may be achieved by deactivating actuatorassembly 220 and allowing the inherent stiffness of flexible coupling414 of tip-tilt-z flexure 230 to restore tip-tilt-z flexure 230 to aninitial state, which causes retraction of micro pick up array mount 250.

During the placement operation described with respect to FIG. 20, heatmay be applied to the array of micro devices 1610. For example, heatingelement 602 may be resistively heated as described above to transferheat through micro pick up array mount 250 into the array ofelectrostatic transfer heads that grip micro devices 1610. Maintainingan elevated temperature of micro pick up array mount 250 in this mannermay avoid some problems that arise from temperature variations in anoperating environment. Micro devices 1610 may be heated continuouslythroughout the placement operation. However, more particularly, microdevices 1610 may be heated after deflection of compliant element issensed and/or after micro devices 1610 are in contact with receivingsubstrate 2101. In an embodiment, each electrostatic transfer head 703in the array is heated uniformly, e.g., to a temperature of 50 degreesCelsius, 180 degrees Celsius, 200 degrees Celsius, or even up to 350degrees Celsius. These temperatures may cause melting or diffusionbetween micro devices 1610 and receiving substrate 2101 to bond themicro devices to the receiving substrate.

Referring to FIG. 25, a schematic illustration of a computer system thatmay be used is shown in accordance with an embodiment of the invention.Portions of embodiments of the invention are comprised of or controlledby non-transitory machine-readable and machine-executable instructionswhich reside, for example, in machine-usable media of a computer system108. Computer system 108 is exemplary, and embodiments of the inventionmay operate on or within, or be controlled by a number of differentcomputer systems including general purpose networked computer systems,embedded computer systems, routers, switches, server devices, clientdevices, various intermediate devices/nodes, stand-alone computersystems, and the like. Furthermore, although some components of acontrol system, e.g., amplifier 1404 and position sensing module 316,have been broken out for discussion separately above, computer system108 may integrate those components directly or include additionalcomponents that fulfill similar functions.

Computer system 108 of FIG. 25 includes an address/data bus 2502 forcommunicating information, and a central processor 2504 unit 2504coupled to bus 2502 for processing information and instructions.Computer system 108 also includes data storage features such as acomputer usable volatile memory 2506, e.g. random access memory (RAM),coupled to bus 2502 for storing information and instructions for centralprocessor 2504 unit, computer usable non-volatile memory 2508, e.g. readonly memory (ROM), coupled to bus 2502 for storing static informationand instructions for the central processor 2504 unit, and a data storagedevice 2510 (e.g., a magnetic or optical disk and disk drive) coupled tobus 2502 for storing information and instructions. Computer system 108of the present embodiment also includes an optional alphanumeric inputdevice 2512 including alphanumeric and function keys coupled to bus 2502for communicating information and command selections to centralprocessor 2504 unit. Computer system 108 also optionally includes anoptional cursor control device 2514 coupled to bus 2502 forcommunicating user input information and command selections to centralprocessor 2504 unit. Computer system 108 of the present embodiment alsoincludes an optional display device 2516 coupled to bus 2502 fordisplaying information.

The data storage device 2510 may include a non-transitorymachine-readable storage medium 2518 on which is stored one or more setsof instructions (e.g. software 2520) embodying any one or more of themethodologies or operations described herein. Software 2520 may alsoreside, completely or at least partially, within the volatile memory2506, non-volatile memory 2508, and/or within processor 2504 duringexecution thereof by the computer system 108, the volatile memory 2506,non-volatile memory 2508, and processor 2504 also constitutingnon-transitory machine-readable storage media.

As used above, “coupling”, “fastening”, “joining”, “retaining”, etc., ofone component against or with another may be accomplished using variouswell-known methods, such as bolting, pinning, clamping, thermal oradhesive bonding, etc. The use of such terms is not intended to belimiting, and indeed, it is contemplated that such methods may beinterchangeable in alternative embodiments within the scope of theinvention.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will be evidentthat various modifications may be made thereto without departing fromthe broader spirit and scope of the invention as set forth in thefollowing claims. The specification and drawings are, accordingly, to beregarded in an illustrative sense rather than a restrictive sense.

What is claimed is:
 1. A mass transfer tool manipulator assembly,comprising: a housing; a tip-tilt-z flexure including a top flexurecomponent, a bottom flexure component, and a flexible couplingconnecting the top flexure component with the bottom flexure component,wherein the top flexure component joins with the housing; an actuatorassembly operably coupled with the bottom flexure component, whereinactuation of the actuator assembly moves the bottom flexure componentrelative to the top flexure component; and a micro pick up array mounthaving a pivot platform coupled with a compliant element, and adisplacement sensor integrated with the compliant element, wherein themicro pick up array mount is coupled with the bottom flexure component.2. The mass transfer tool manipulator assembly of claim 1, wherein thetop flexure component and the bottom flexure component each comprise aflange.
 3. The mass transfer tool manipulator assembly of claim 1,further comprising a distribution plate coupling the actuator assemblywith the bottom flexure component.
 4. The mass transfer tool manipulatorassembly of claim 1, further comprising a base laterally around thepivot platform, wherein the compliant element is between the pivotplatform and the base, wherein the compliant element is coupled with thepivot platform at an inner pivot and coupled with the base at an outerpivot.
 5. The mass transfer tool manipulator assembly of claim 4,wherein the compliant element comprises a beam, wherein the displacementsensor comprises a strain gauge, and wherein the strain gauge isattached to the beam.
 6. The mass transfer tool manipulator assembly ofclaim 5, further comprising a reference strain gauge adjacent to thestrain gauge on the beam, wherein the strain gauge and the referencestrain gauge provide adjacent legs in a half Wheatstone bridge.
 7. Themass transfer tool manipulator assembly of claim 3, further comprising atemperature sensor on the pivot platform.
 8. The mass transfer toolmanipulator assembly of claim 7, further comprising a heating elementover the pivot platform.
 9. The mass transfer tool manipulator assemblyof claim 4, further comprising a base operating voltage contact on thebase in electrical connection with a pivot platform operating voltagecontact on the pivot platform.
 10. The mass transfer tool manipulatorassembly of claim 4, further comprising a base clamp contact on the basein electrical connection with a clamp electrode at a bonding site on thepivot platform.
 11. The mass transfer tool manipulator assembly of claim4, further comprising a bonding site on the pivot platform, wherein thebonding site comprises a metal selected from the group consisting of:gold, copper, and aluminum.
 12. The mass transfer tool manipulatorassembly of claim 8, further comprising a displacement sensor contact onthe base in electrical connection with the displacement sensor.
 13. Themass transfer tool manipulator assembly of claim 12, further comprisinga position sensing module in electrical connection with the displacementsensor through the displacement sensor contact.
 14. The mass transfertool manipulator assembly of claim 13, wherein the displacement sensorcontact is in electrical connection with the position sensing modulethrough a flex circuit.
 15. The mass transfer tool manipulator assemblyof claim 13, wherein the displacement sensor contact is in electricalconnection with the position sensing module through a spring contact.16. The mass transfer tool manipulator assembly of claim 13, furthercomprising an insulation plate between the heating element and theposition sensing module, wherein the base is coupled with the insulationplate, and wherein the insulation plate couples the micro pick up arraymount with the distribution plate.
 17. The mass transfer toolmanipulator assembly of claim 1, further comprising a micro pick uparray having a substrate supporting an electrostatic transfer head, themicro pick up array joinable with the pivot platform.